Oil Furnace Roar Comes In and Out

We're in the middle of a cold spell in the North East. I have an oil furnace. It is heating the water for the heating system okay. However, it is making strange noise.

When the heating system is running, normally it makes a nice solid roar. However, now it goes back and forth between relative quiteness and the roar. (Almost as if its taking a breath.) The flame is solid and strong the entire time. And, as I said, there is hot water in the radiators.

Does anyone have any ideas as to what it might be?

I have a service scheduled for next week. Should I wait for the service, or should I get someone sooner? And do you think its okay to run the furnace?

There is a faint smell (combustion) when you open the door to the basement. Something we didn't have before. The carbon monoxide detector is not at alarm levels.

I do notice that the draft regultor door is open about as far as it can be. It is set to between -0.05 and -0.06. However, the draft regulator door is on top of the stack pipe. It is not a round draft regulator. The draft regulator door is at an angle of 45%, with the weight on the top part of the door and the opening at the lower end. And basically the door cannot open any more because the weight is against the ceiling (preventing it from going any further). For all I know, this could be how it normally operates. I haven't had any issues with this, so I've never paid any attention to it.

Do you know what kinds of issues could be causing these issues? Should I consider calling a chimney sweep to see if there is a partial blockage?

You will need a draft meter to check the draft while the unit is off and when it is running, both at the breech and at the chimney inlet but I suspect that you have a combustion issue, probably fuel delivery related.

Thanks Peter for your help. I left this to the experts and got someone in today. Last night, I was mainly looking for reassurance that there wasn't a serious issue (and I wasn't risking the safety of my two babies).

I wanted to follow up and let people know the resolution (in case someone else has the same issue and wants to know what it was). As Peter figured, it was an issue with the oil getting to the burner. It was actually a blockage in the line from the oil tank to the furnace.